It is often beneficial for an aircraft to be able to take off and land on very short runways. This is especially true for military aircraft that often must take off and land in very short distances whether in combat or out of combat. For instance, aircraft taking off the deck of an aircraft carrier must take off and land on a runway no more than about three hundred feet. This means for many military aircraft it's optimal that it be able to generate enough lift in a very short distance to overcome its weight. It also means that the aircraft must be able to be operated at very low speeds in order to effectively land in such a short distance. Currently most military cargo aircraft need a minimum of two thousand feet to effectively takeoff and land. Optimally a military cargo aircraft would be able to take off and land over much shorter distances, but that would require increasing the lift of the aircraft while as well as the low speed control of the aircraft. Unfortunately, most cargo aircraft are very difficult to control at low speeds and operating a cargo aircraft at low speeds often results in accidents due to stalling.
Stalls are experienced as a sudden reduction in lift when the critical angle of attack of a wing is exceeded. Often this is a result of slowing the aircraft below the minimum stall speed for a given angle of attack during level flight. When this occurs, many aircraft will start to lose elevation and cause the nose to pitch down because the wing is no longer producing enough lift to support the aircraft's weight. To recover from a stall in a fixed wing aircraft, the angle of attack must be reduced and the speed of the aircraft must be increased so that airflow over the surfaces of the wing system is normalized. Some aircraft are equipped with systems that allow the angle of incidence of the aircraft to be changed, which may be used to increase or decrease the angle of attack without pitching the nose of the aircraft. Additionally, some aircraft allow the sweep of the wings to be altered, which may increase or decrease the critical angle of attack of an aircraft without pitching the nose or increasing the speed due to an increase in the lift generated by the aircraft by sweeping the wings forward. Various other technologies have been created to reduce the stall speed of an aircraft with mixed success. One such technology is vortex generators.
Vortex generators, which look like small fins perched on the surfaces of the aircraft, improve an aircraft's aerodynamic performance by delaying boundary layer separation. The boundary layer is a small layer of air that surrounds the aircraft and is somewhat slow moving compared to the aircraft as it moves through the air. Because of this, as the aircraft moves through the air, the boundary layer falls behind the aircraft and creates a wake, which creates drag. Drag acts on the aircraft by slowing the aircraft down and reduces the amount of lift force effectively generated by the aircraft. Vortex generators may be used to delay the separation of the boundary layer from the aircraft by creating minor turbulence in the form of vortices. This turbulence gives the boundary layer more energy, which allows it to separate from the aircraft system at a later time. This later separation results in a smaller wake, resulting in less drag acting on the aircraft. Smaller wake also effectively increases the lift generated by the aircraft, which both decreases the speed needed to overcome the weight of the aircraft to achieve take off and decreases the minimum stall speed. In effect, an aircraft having a vortex generator may both take off and land over shorter distances.
Currently, vortex generators are attached to the aircraft in a permanent orientation. This isn't always advantageous because the effectiveness of vortex generators is increased or decreased depending on the angle of attack it creates with the upcoming flow of air. For instance, a vortex generator having a high angle of attack with the upcoming airflow may create a large vortex, but this may take a lot of energy to create, thus creating more friction drag that it reduces drag caused by flow separation. Alternatively, a vortex generator having an angle of attack parallel to upcoming flow of air will produce very small vortices, which will have a minimal effect on drag caused by flow separation. Additionally, the effectiveness of vortex generators varies with the angle of attack of the wings of the aircraft. This means that current aircraft having vortex generators may only notice the reduced drag and improved flight performance under a very narrow set of circumstances.
Accordingly, a need exists in the art for an improved aircraft system having an adjustable vortices device that may take off and land over short distances as well as be able to fly over long distances without having to stop and refuel.